This light-specific phenomenon is a frequently recurring theme which is dealt with in various reports. But what exactly causes it? The "blue edge" refers to the light component in the area of the cut-off line which frequently has a bluish white light colour.
The characteristic and intensity of the edge depends on several factors. Here are some examples:
1. Lens material of projection module
The light refraction or diffusion varies depending on the material of the focusing lens, which can be glass, polymethylmethacrylate, or polycarbonate, for example. This affects the light colour.
2. Position of the light source in relation to the bulb shield
Light sources are mounted at different distances and positions (vertically) in relation to the bulb shield. Light is therefore "refracted" or "diffracted" differently at the bulb shield.
3. Reflector or projector-type system
The way in which light is emitted or focused also has an effect on the cut-off line. The blue edge of a reflector-type system is normally not as pronounced as that of a projector-type system. The reason for this is the so-called "degree of hardness". This refers to the light-to-dark transition (cut-off line). Projector-type systems have a higher degree of hardness due to the bulb shield.